The monthly survey is likely to be unusually scrutinized by financial markets because steady job growth could confirm expectations that the Federal Reserve will scale back its bond-buying stimulus at a Sept. 17-18 meeting.

"The pace of employment growth in August is likely to be a key factor in the Fed's decision on tapering" the program, David Berson, chief economist of Nationwide Insurance, said in a research note.

Thursday's positive reports could also figure into the Fed's decision. The number of Americans applying for jobless benefits for the first time fell to 323,000 from 332,000. The four-week average, which smooths out volatility, dropped 3,000 to 328,500 - lowest since before the 2007-08 recession.

Midsize businesses added 74,000 jobs; small businesses, 71,000; and large companies, 32,000. That marks a possible shift - small firms had solidly led job gains much of the year.

Among industry sectors, professional and business services added 50,000 jobs, followed by trade, transportation and utilities with 40,000.

"There is little evidence that fiscal austerity and health care reform have had a significant impact on the job market," says Mark Zandi, chief economist of Moody's Analytics, which helps ADP conduct the survey.

Also, a measure of service-sector activity jumped sharply in August, to 58.6 from 56. A reading above 50 indicates the sector is expanding, while below means it's shrinking. A gauge of employment also rose dramatically to 57 from 53.2, the Institute for Supply Management said.

"These are very positive data for the recovery," Jim O'Sullivan, chief U.S. economist of High Frequency Economics, said in a research note.

One less-encouraging report showed that the number of layoffs employers announced last month jumped to 50,462, up from about 38,000 in July and 32,000 in August 2012, according to outplacement firm Challenger Gray and Christmas. The cuts, however, were largely driven by falling global demand for mining equipment, Challenger said.

"While that definitely has an impact on the economy, it is not as worrisome as an overall slowdown in construction or manufacturing," said Challenger CEO John Challenger.